Methodology for a practical flat panel format holographic display utilizing the narrow hologram and holodot concepts

ABSTRACT

An apparatus for creating a holodot comprising of a low resolution 2 dimensional spatial light modulator (SLM) and two crossed striped high resolution spatial light modulators. The first SLM creates a 2D image and the second two focus the light into an observer&#39;s pupil.

CROSS REFERENCE TO RELATED APPLICATIONS

The present patent application is a formalization of a previously filedprovisional patent application entitled “A Methodology For a PracticalFlat Panel Format Holographic Display Utilizing The Narrow Hologram AndHolodot Concepts,” filed Mar. 13, 2014, as U.S. patent application Ser.No. 61/952,563 by the inventor(s) named in this application. This patentapplication claims the benefit of the filing date of the citedprovisional patent application according to the statutes and rulesgoverning provisional patent applications, particularly 35 USC §119 and37 CFR §1.78. The specification and drawings of the cited provisionalpatent application are specifically incorporated herein by reference.

COPYRIGHT

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The owner has no objection tothe facsimile reproduction by anyone of the patent disclosure, as itappears in the Patent and Trademark Office files or records, butotherwise reserves all copyright rights whatsoever.

FIELD OF INVENTION

This invention is related to synthesizing of a holodot from coherentlaser light. An apparatus comprising of a low resolution 2 dimensionalspatial light modulator (SLM) and two crossed striped high resolutionspatial light modulators. The first SLM creates a 2D image and thesecond two focus the light into an observer's pupil.

BACKGROUND

The problem with existing stereo 3D is eye strain caused by skew and eyetracking focus disconnect. Any body who has tried to market 3D over thepast 130+years has become painfully aware that one can not market awayEye strain.

The logical solution would be to just create a Holographic display.Conventional wisdom would dictate this would require a panel with wavelength pixel spacing. Each with the ability to control both the phaseand amplitude of its sourced light. This would require hundreds ofbillions of pixels. A very impractically to do large number. The mistakethat convictional wisdom makes is that it neglects to realize that oneonly has to worry about the light field at the viewer's eyes pupils.This means two things. First, one only has to create a hologram at theeyes pupils. And second, one can ignore any light that falls out sidethese pupils.

The invention given here utilizes these two concept to create aholographic display that only requires a panel with standard pixeldensity. That is 1900×1080 for high definition.

SUMMARY

Referring to FIG. 1, items 101,102, and 103 comprise the main basiccomponents of this flat panel holographic display concept. The purposeof item 101 is to provide parallel Laser light for item 102. It providesthe same function as a laser/ telescope beam expander combination exceptin a flat package for flat panel compatibility. Item 102 is known asspacial light modulator. It consists of a standard density pixel arraywere each pixel can modulate the light from 101 in both phase andamplitude. It creates a narrow angle hologram for Items 103. The twoitems comprising 103 create a lens variable in both focal length andposition. It focuses the light of the narrow angle hologram from 102down to a holodot 104 at the pupil of eye 105.

The display system multiplexes between the three main colors and bothpupils of the viewer to create the full illusion. If there are multipleviewers then the display would also have to multiplex between theviewers.

The display has two cameras looking at the viewer. Through the use ofimage processing software, the system will track the three dimensionalposition of each pupil. This information will be used to control thevariable lens 103 so that the holodot 104 will always be at the pupil ofeye 105 regardless of the viewers head position.

The pupil position will also be used to control the content of thespacial light modulator 102 so that the holodot 104 is the correctportion of a nonexistent full hologram plane located at a position whereit coincides with the pupil of eye 105. To the viewer, it will look likea full hologram.

For a computer generated object, the computer would have to constantlyholographically re-render the object to keep up with eye 105's position.This is doable and probably the preferred approach for a sceneconsisting of a finite number of generated objects.

For capturing a real scene, many two dimensional pictures at differentangles would have to be taken and stored. The display system would haveto analyze these pictures along with eye 105's position to create theholodot 104. Some day this might actually be done. But, for now it is avast over kill. In stead we could take advantage of existing stereo 3Dtechnology. This is important because the expertise and hardware allready exists for the production and distribution of stereo 3D contentalong with a library of actual content.

For a standard 3D display, the focused image plain (FIP) alwayscoincides with the screen of the display. If the viewers eyes aretracking an imaged object which is not at the screen then the eyes whichnaturally want to be focusing at the imaged object's distance, areunnaturally being forced to focus at the screen's distance. This causeseye strain. The holographic display in FIG. 1 can place the FIP at anydistance behind, at, or in front of the display. So, it can and willplace the FIP at the imaged object's distance thus, eliminating thissource of eye strain for good.

The display system will determine where to place the FIP using themeasured distance between the viewers pupils and or basic camerainformation stored with each frame.

For a standard 3D display, the separation between the left and right eyeviews are always perfectly horizontal relative to the display. This isfine as long as the viewer keeps his eyes perfectly horizontal at alltimes. If the viewer tilts his head then one eye will be force to lookup while the other one will be force to look down. This is unnatural andwill also cause eye strain. Because the display system knows thedistance of the imaged object which the viewer is looking at, it canslide the left and right images around so that the separation tilt anglematches that of the viewers head. Thus eliminating another source of eyestrain.

The left and right images can also be slid around enlarged or contractedto make the imaged object which the viewer is looking at appear to stayfixed in space regardless of the viewers head movement. This willsupport the illusion of a hologram from a set of stereo images.

With these and possibly other holographic enhancements of standardstereo 3D content, the question is, what is the difference betweenenhanced stereo 3D and a full hologram. Well, if one is viewing anenhanced 3D object and decides to move his head to get a better look atthe side of the object, the object will stay where it is in space, but,it will conveniently rotate to keep showing the viewer the same face.Just like, the moon always points the same face towards the earth. Thisis because this is the only view it has. Besides being a cute nuisance,nobody is going to get eye strain from this. In fact for moving contentit would be almost impossible to determine if that rotation was from theviewers head movement or camera content object movement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an apparatus capable of generating a holodotaccording to a preferred embodiment. It also contains the holodot and anobserver's eye.

FIG. 2 is a top view of evenly spaced phase coherent light sources.

FIG. 3 is a side view of the 2 dimensional spatial light modulatorgenerating 2 image points. It also includes an observer's eye.

FIG. 4 is a front view of a single modulating cell of the 2 dimensionalspatial light modulator.

FIG. 5 is a side view of the 2 dimensional spatial light modulator, witha spherical lens, generating 2 image points. It also includes theholodot and an observer's eye.

FIG. 6 is a side/edge view of two cylindrical lens one verticallyoriented and the other horizontally oriented.

FIG. 7 is a front view of a vertically striped liquid crystal phasemodulating panel. The figure also includes a front and top view of anenlarged section of this panel.

FIG. 8 is a side view of the three spatial light modulators generating amultitude of holodots. It also contains an observer's eye.

FIG. 9 is a front view of a single modulating cell, with serrated edges,of the 2 dimensional spatial light modulator.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

Multiple Images

Before one can began any kind of detailed description, one must firstunder stand the concept of an image. Referring to FIG. 2, each of thedashes of item 201 is a uniformly illuminated correlated parallelmonochromatic light source. Each point along a dash is a point source oflight. Each having the same wave length, phase and intensity. Each ofthe dashes is identical. This is identical to a beam expanded laserlight source with a grading. Where each dash of 201 is an opening inthat grading.

The spread 208 of the light from each of these dash light source isrelated to width 204 of the source. The smaller the width 204 thegreater the spread 208. The arrows 207 show the primary direction oflight coming from the sources 201. It is perpendicular to sources 201because that is the angle at which the phases of the light from each of201's sources is the same. A viewer looking in the direction of arrow209 would see a single point source at infinity.

Arrows 205 show another direction of light coming from the sources 201where the phases of the light from each of 201's sources is the same.This is because, at this angle, the difference in path length betweenadjacent sources 202 is exactly one wave length. A viewer looking in thedirection of arrow 206 would also see a single point source at infinity.

If a viewers angular field of view is large enough, he will see thepoint source at infinity in the direction of 209 and an image pointsource at infinity in the direction of 206. In fact, he would see animage at every angle where the delta 202 is an integral multiple of thewave length.

The number of images one can see depends of the light spread 208. Thewider the width 204 of the source the narrower the spread 208 and thefewer images a viewer sees. Ultimately when the width 204 equalsdistance 203 between the sources, the viewer will only see the singleprimary point source at infinity and no images.

The Narrow Angle Hologram

Referring to FIG. 3, item 301 is a spacial light modulator with astandard pixel resolution. Each pixel can modulate the coherent laserlight 304 in both amplitude and phase. This can be done using liquidcrystal technology.

By modulating the light 304, the panel 301 can create the same lightpattern at the plane of 301 that a pixel point source 303 located in 3Dspace would create if it were real.

Since any scene can be represented by finite number of pixel pointsourced (303 typical), One can program the panel 301 with a linearcombination of each pixel's light pattern to create the light patternfor the entire scene.

The angular spread 302 of the light coming from the panel 301 will belimited to very small angles because of the low pixel resolutionrelative to the size of a wave length of light. Hence the name “narrowangle hologram”.

For holographically enhanced 3D, at any one time, all the pixels are inthe same plane. For this case, calculating the light pattern to beloaded into the panel 301 could be done using an easer math operationcalled a convolution as apposed to calculating and adding in the lightpattern for each and every 3D space pixel separately. The math involvedin creating the full light pattern loaded into the panel 301 utilizescomplex numbers and is straight forward for anyone with the proper mathback ground. For this reason the math is not patentable and, there for,will not be discussed here.

FIG. 4 shows the front view of a typical pixel of the spacial lightmodulating panel 301. We have learned form our previous discussion onmultiple images that it is best to maximize the active illuminated pixelregion 402 and minimize the dark dead regions 401 between the pixels inorder to minimize multiple images. Beam expander techniques can be usedto help minimize these 401 dark zones.

We have also learned from the multiples images discussion thatmaximizing region 402 will minimize the angular light spread 302 of FIG.3. This means that, as an example, all though eye 306 can see pixelimage 305 it would not be able to see pixel image 303. The eye wouldhave very narrow tunnel vision and could only see a very small portionof the scene created by the panel 301.

The Holodot

Referring to FIG. 5, to solve this tunnel vision problem, lens 502 isplaces in front of the modulating panel 501 to converge the lighttowards eye 506 creating the holodot 507 at the focal point of lens 502.If the pupil of eye 506 is at this holodot, Then the eye will be able tosee all of the images created by the panel 501 form the laser lightsource 504. Thus, solving the tunnel vision problem.

There are two draw backs to this lens. First, the lens 502 will distortthe scene created by the panel 501. The lens would re image a typical 3Dspatially located pixel 505 to the location of 503. This distortionissue is easily solved by mathematically pre inverse distorting thescene before it is loaded into panel 501. When the eye views thisinverse distorted scene through the distorting lens 502, it will see theoriginal undistorted scene.

The Variable Lens

The second draw back is that for fixed lens, the position of the holodot507 is fixed. This means that the eye would have to stay at this oneholodot position at all times. Besides the unacceptable requirement ofhaving the viewer keep his head at one position at all times, this wouldmake multiplexing between the eyes impossible.

The obvious solution is to make lens 502 variable in both focal lengthand, up down left right, position. The first step in this solution, isto realize that lens 502 can be replaced by two cylindrical lenses 601and 602 as seen in FIG. 6. Lens 601 is curved along the vertical axisand lens 601 along the horizontal axis.

The second step is to realize that a cylindrical lens can be made with astriped liquid crystal panel 701 of FIG. 7. Each typical liquid crystalcell stripe 707 as seen in enlarged section 705 can be programmed toshift the phase, of light passing through it, an arbitrary amount. Byprogramming the cells with the correct combination of phase shifts onecan create a cylindrical lens with an arbitrary position and focallength.

FIG. 8 shows the results in one of the dimensions of replacing lens 502of FIG. 5 with the two striped liquid crystal panels 802. One would havevertical strips and the other horizontal.

As we have learned form our earlier discussion of multiple images, thisset up would produce multiple holodots 804 typical . The spacing 806between the holodots would depend on the spacing 706 between the liquidcrystal stripes (LCS). The smaller the 706 spacing the larger the 806spacing.

For the minimal holodot spacing 806 and greater, where only one holodotlands on the pupil, the viewers eye 805 would only see the primary sceneimage and no other multiples. The pupil is a spacial filter removingmultiples images. This minimal spacing 806 requires about 10 thousandliquid crystal stripes in the panels 802.

For the multiplexing process between eyes to work, while one eye 805typical is seeing a holodot, the other eye must either be shuttered or,its pupil must be in a dead zone between holodots. For shuttering, thesame standard 3D shuttering glasses already developed and in productioncould be used.

In a three dimensional version of FIG. 8, the holodots 804 form a twodimensional grid pattern in a plane at the pupil. This grid has twohorizontal holodot free dead zones, one above and one below the pupil.So, if one tilts the grid by tilting the display, at the right angle,one can place a dead zone at one pupil while keeping the other pupil onthe holodot.

This could be done by mounting the display on a gimbal which wouldrotate it to maintain the proper angle difference between the holodotgrid and the pupil axis regardless of head movement. At the same timethe display content would be counter rotated so that the viewer wouldsee the same unchanged scene regardless of display angle or rotation.

The display would not change in rotation for multiplexing between thepupils of a single viewer.

The display would not be able to rotate fast enough to multiplex betweenviewers. So, this method would only work for a single viewer.

Both of these shutter or rotation methods would only be a possiblecompromise for early generation displays.

If you increase the number of stripes to about one hundred thousand, Thespacing distance 706 of the stripes would decrease enough to cause theseparation distance 806 of the holodots 804 to be great enough so that,while the main holodot is on one pupil, the first holodot image wouldfall on the out side the viewer's other pupil. Although this means thata single viewer would not have to ware any 3D type shutter glasses,multiple viewers would, because the holodot spacing 806 is not enoughfor the first holodot image to fall on the out side of a group ofviewers.

If instead of making the spacing 706 of the stripes the same, one variesthem in a pseudo random manner, then, although the primary holodot wouldbe unchanged, all the other holodot images will be blurred into one bigconstant illumination.

To explain this lets refer back to FIG. 2. A secondary image is formedbecause the angle of arrows 205 is the same for each pare of lightsources 201. The angle is the same because both the separation distance203 and wave length distance 202 are the same. Now is one if keeps 202the same while varying 203 then the angles will vary resulting in ablurred non primary image.

Most of this blurred image light either lands on the viewers face ormisses the viewer all together and is thus unnoticed by the viewer. Itis only the small portion of light that hits the viewer pupil which isadded as a constant illumination to the scene.

The attenuation of this constant illumination relative to the averageillumination of the scene is equal to the square of the quotient of thepupil diameter divided by the non blurred distance 806 between theholodots (FIG. 8). For 100 k striped 802 panels, this constant unwantedillumination works out to be approximately only a very tolerable 1% ofthe average illumination.

The effects of this unwanted constant illumination could be minimized bynumerically subtraction the calculated average illumination of the scenefrom the scene before processing and loading it into panel 801.

When the spacing 706 (FIG. 7) of the stripes approaches a wave length oflight, it won't matter. Because the non primary holodots will be at sucha great angle that none of the viewers will see it.

Referring to FIG. 7, Item 702 is a top view of the panel 701 showing acylindrical curvature in front of each liquid crystal phase shiftingstripe. This is needed for non wave length 706 spacings to create thelight spread 703 necessary for a useful angle of view.

Improvement

Referring to FIG. 4 of a typical pixel of the spacial light modulator, Asmooth transition between a typical pixel 402 and its neighbor willresult in a better picture quality than the abrupt ones shown here.

FIG. 9 shows a method for obtaining a smooth transition between pixels.Here the straight line borders 401 typical of FIG. 4 are replaced by theserrated borders 902 typical. The scattered light caused by the abruptborders of the serrations will fall outside the viewers pupil. Theviewer will only see a smooth transition of the mixing of the pixels inthe overlap region.

As with the pixel of FIG. 4. This serrated border pixel can be builtusing beam expander techniques.

The Flat Beam Expander

Referring to FIG. 1, as all ready mentioned, the flat beam expander 101provides the same function as a laser/telescope beam expandercombination except in a flat package.

It can be made using the same techniques used in beam splitters. This isbecause we are using coherent laser light and all the phase andamplitude imbalances can be corrected for in the spacial light modulator102.

Calibration

There are two types of calibrations that will be mentioned here. Thefirst is for component manufacturing error and age, temperature, and anyother factor drift error.

Each of these display system has a powerful processor, two cameras, andjust about every thing can be independently adjusted by the processor.All the necessary hardware is already there for component calibration.It's just a matter of software.

The second is for the viewer's eye balls. As mentions earlier, themeasured distance between the viewer's pupils can be used to determinethe distance form the viewer of the object which he focused on. This,however, can only be done if one knows both the diameter viewer's eyeballs and the distance between the axis's of rotation of the eye balls.

To get this information one can take advantage of the fact that thedirector of a movie determines what a viewer will be concentrating on orlooking at. This information can be transferred to the display systemthrough the basic camera information stored with each frame. This wouldinclude lens separation, angle of inward pointing of the lenses, totalangular field of view, and focus ring setting.

Initially the display would use this information to set distance offocused image plane (FIP). The display would then log several distancesof the FIP verses pupil separations. Once the display has enough of thisinformation to accurately calculate both the diameter viewer's eye ballsand the distance between the axis's of rotation of the eye balls, itwill do so, and then change over to using pupil distance to set thedistance of the FIP.

The display can also use facial recognition to identify a repeat viewerso that, it can skip this calibration mode.

The foregoing explanations, descriptions, illustrations, examples, anddiscussions have been set forth to assist the reader with understandingthis invention and further to demonstrate the utility and novelty of itand are by no means restrictive of the scope of the invention. It is thefollowing claims, including all equivalents, which are intended todefine the scope of this invention.

What is claimed is:
 1. An apparatus responsive to coherent laser lightand operative to generate at least one holodot at an observer's pupil,comprising: (a) a first spatial light modulator panel; (b) a secondspatial light modulator panel comprising the modulating cells elongatedin the same direction with the ratio of the elongated dimension to thenon elongated dimension greater than 10; (c) a third spatial lightmodulator panel comprising the modulating cells elongated in the samedirection with the ratio of the elongated dimension to the non elongateddimension greater than 10; and (d) the direction of the modulatingcell's elongation of the second spatial light modulator panel isdifferent form the direction of the modulating cell's elongation of thethird spatial light modulator panel.
 2. An apparatus responsive tocoherent laser light and operative to generate at least one holodot,comprising: (a) a first spatial light modulator panel; (b) a secondspatial light modulator panel comprising the modulating cells elongatedin the same direction with the ratio of the elongated dimension to thenon elongated dimension greater than 10; (c) a third spatial lightmodulator panel comprising the modulating cells elongated in the samedirection with the ratio of the elongated dimension to the non elongateddimension greater than 10; and (d) the direction of the modulatingcell's elongation of the second spatial light modulator panel isdifferent form the direction of the modulating cell's elongation of thethird spatial light modulator panel.
 3. An apparatus responsive tocoherent laser light and operative to generate at least one holodot atan observer's pupil, comprising: (a) a first spatial light modulatorpanel; (b) a second spatial light modulator panel comprising themodulating cells elongated in the vertical direction with elongationextending from the top of the panel to the bottom of the panel; and (c)a third spatial light modulator panel comprising the modulating cellselongated in the horizontal direction with elongation extending from oneside of the panel to the other side of the panel.
 4. An apparatusresponsive to coherent laser light and operative to generate at leastone holodot at an observer's pupil, comprising: (a) a first spatiallight modulator panel; (b) a second spatial light modulator panelcomprising liquid crystal phase only modulating cells elongated in thevertical direction with elongation extending from the top of the panelto the bottom of the panel; and (c) a third spatial light modulatorpanel comprising liquid crystal phase only modulating cells elongated inthe horizontal direction with elongation extending from one side of thepanel to the other side of the panel.
 5. A method for generate at leastone holodot at an observer's pupil using an apparatus responsive tocoherent laser light, said method comprising: (a) spatially modulatinglight with a first spatial light modulator panel; (b) spatiallymodulating light with a second spatial light modulator panel comprisingthe modulating cells elongated in the same direction with the ratio ofthe elongated dimension to the non elongated dimension greater than 10;(c) spatially modulating light with a third spatial light modulatorpanel comprising the modulating cells elongated in the same directionwith the ratio of the elongated dimension to the non elongated dimensiongreater than 10; and (d) the direction of the modulating cell'selongation of the second spatial light modulator panel is different formthe direction of the modulating cell's elongation of the third spatiallight modulator panel.
 6. A method for generate at least one holodotusing an apparatus responsive to coherent laser light, said methodcomprising: (a) spatially modulating light with a first spatial lightmodulator panel; (b) spatially modulating light with a second spatiallight modulator panel comprising the modulating cells elongated in thesame direction with the ratio of the elongated dimension to the nonelongated dimension greater than 10; (c) spatially modulating light witha third spatial light modulator panel comprising the modulating cellselongated in the same direction with the ratio of the elongateddimension to the non elongated dimension greater than 10; and (d) thedirection of the modulating cell's elongation of the second spatiallight modulator panel is different form the direction of the modulatingcell's elongation of the third spatial light modulator panel.